1. Field of the Invention
This invention relates to chemically modified fibers and their use as a pH-regulating material.
2. Statement of the Related Art
Absorbent materials, particularly those for medical, hygienic, cosmetic, or similar personal use, usually consist of hydrophilic cotton linters (i.e. absorbent cotton), viscose fibers, flexible foams, or the like.
Where such materials come into direct contact with parts of the body, it is advantageous to provide them with additives which positively affect the pH of the body at the point of contact, particularly by lowering or maintaining it. This assists in preventing irritation and reduces susceptibility to diseases, particularly those caused by alkaliphilic microorganisms.
An example of a known material of this type is disclosed in German Patent Application No. 23 09 575 which proposes impregnating tampons with substances which maintain a vaginal acid pH, such as glycogen, sugar, Doederlein bacteria, all of which help form lactic acid through Lactobacillus acidophilus. However, additives such as the above are not effective for their intended purpose, since the alkaline environment of the vagina during menstruation seriously inhibits the growth of L. acidophilus.
It has also been proposed in German Patent Application No. 23 09 575 (above) to impregnate with lactic acid per se, as well as citric acid, and the like. However, because of the strong buffer effect of menstrual fluid, and because of the relatively small amount of acid with which a tampon may be impregnated, the beneficial effect of the impregnant is exhausted after only a small accumulation of menstrual blood.
U.S. Pat. No. 4,431,427 and corresponding German Patent Application No. 32 36 768 describe tampons containing one or more substances which, when the tampon is in use, produce and maintain a pH in the range 2.5 to 4.5 and thus prevent the growth of pathogenic bacteria. Substances of the type in question are disclosed as including monomeric and/or polymeric, physiologically compatible carboxylic acids, such as citric acid, malic acid, tartaric acid or lactic acid. Tampons of this type also have the disadvantage that the strong buffer effect of the body fluids limits the acidifying effect of the acids introduced into the tampon.
U.S. Pat. No. 3,187,747 describes absorbing fiber materials having ion-exchange properties where the composition is a multicomponent polymer system. Polymer components having fiber-forming properties, for example textile fibers, are present alongside other polymers having acidifying properties, for example carboxymethyl cellulose, in the form of "polymer alloys" which may be obtained from homogeneous solutions of suitable polymers. The heterogeneity of the starting polymers means 30 that the processing of the polymer alloys into the required hygiene aids involves additional process steps, such as solvent exchange drying, in order to degelatinize the fibers and to prevent them from sticking to one another during the drying process. In addition, fibers of the type in question are frequently treated with cation-active softeners and lubricants to improve their processing properties, although this adversely affects the acidifying properties of the fiber material.
Another process in which a known material, a modified viscose fiber, is blended with a substance which, in use, produces a reduction in the pH is described in U.S. Pat. No. 4,044,766 and corresponding German Patent Application No. 27 09 132. Cellulose fibers are reacted with monochloroacetic acid to form carboxymethyl cellulose. The resulting carboxymethyl cellulose fibers have an average degree of substitution of from 0.4 to 2.0. This etherification process is carried out on the "finished" fiber. The disadvantage of this known process is that the subsequent etherification step yields fibers having a slimy surface which are unsuitable for medical, cosmetic, or similar applications. In addition, materials produced from fibers of this type only contain free carboxyl groups at the fiber surface, with the result that cationic substances present in body fluids bring about a rapid and complete deactivation of the pH-regulating capabilities of the fiber.